fix(badge): incorrectly setting aria-describedby (#9957)

* With the current setup, the badge component will set an `aria-describedby` message that doesn't correspond to the actual description, because it does the describing before its description has been updated. These changes make it so it uses the actual description.
* Fixes the aria description not being removed once the badge is destroyed.
* Cleans up the badge testing setup.

src/lib/badge/badge.spec.ts

@@ -1,132 +1,141 @@
-import {ComponentFixture, TestBed, async} from '@angular/core/testing';
+import {ComponentFixture, TestBed, fakeAsync} from '@angular/core/testing';
 import {Component, DebugElement} from '@angular/core';
 import {By} from '@angular/platform-browser';
 import {MatBadge, MatBadgeModule} from './index';
 import {ThemePalette} from '@angular/material/core';
 
 describe('MatBadge', () => {
   let fixture: ComponentFixture<any>;
-  let testComponent: BadgeWithTextContent;
-  let badgeNativeElement;
+  let testComponent: BadgeTestApp;
+  let badgeNativeElement: HTMLElement;
+  let badgeDebugElement: DebugElement;
 
-  beforeEach(async(() => {
+  beforeEach(fakeAsync(() => {
     TestBed.configureTestingModule({
       imports: [MatBadgeModule],
-      declarations: [BadgeWithTextContent],
+      declarations: [BadgeTestApp],
     }).compileComponents();
-  }));
 
-  beforeEach(() => {
-    fixture = TestBed.createComponent(BadgeWithTextContent);
+    fixture = TestBed.createComponent(BadgeTestApp);
     testComponent = fixture.debugElement.componentInstance;
     fixture.detectChanges();
+
+    badgeDebugElement = fixture.debugElement.query(By.directive(MatBadge));
+    badgeNativeElement = badgeDebugElement.nativeElement;
+  }));
+
+  it('should update the badge based on attribute', () => {
+    let badgeContentDebugElement = badgeNativeElement.querySelector('.mat-badge-content')!;
+
+    expect(badgeContentDebugElement.textContent).toContain('1');
+
+    testComponent.badgeContent = '22';
+    fixture.detectChanges();
+
+    badgeContentDebugElement = badgeNativeElement.querySelector('.mat-badge-content')!;
+    expect(badgeContentDebugElement.textContent).toContain('22');
   });
 
-  describe('MatBadge Text', () => {
-    let badgeDebugElement: DebugElement;
+  it('should apply class based on color attribute', () => {
+    testComponent.badgeColor = 'primary';
+    fixture.detectChanges();
+    expect(badgeNativeElement.classList.contains('mat-badge-primary')).toBe(true);
 
-    beforeEach(() => {
-      badgeDebugElement = fixture.debugElement.query(By.directive(MatBadge));
-      badgeNativeElement = badgeDebugElement.nativeElement;
-      fixture.detectChanges();
-    });
+    testComponent.badgeColor = 'accent';
+    fixture.detectChanges();
+    expect(badgeNativeElement.classList.contains('mat-badge-accent')).toBe(true);
 
-    it('should update the badge based on attribute', () => {
-      let badgeContentDebugElement = badgeNativeElement.querySelector('.mat-badge-content');
+    testComponent.badgeColor = 'warn';
+    fixture.detectChanges();
+    expect(badgeNativeElement.classList.contains('mat-badge-warn')).toBe(true);
 
-      expect(badgeContentDebugElement.textContent).toContain('1');
+    testComponent.badgeColor = undefined;
+    fixture.detectChanges();
 
-      testComponent.badgeContent = '22';
-      fixture.detectChanges();
+    expect(badgeNativeElement.classList).not.toContain('mat-badge-accent');
+  });
 
-      badgeContentDebugElement = badgeNativeElement.querySelector('.mat-badge-content');
-      expect(badgeContentDebugElement.textContent).toContain('22');
-    });
+  it('should update the badge position on direction change', () => {
+    expect(badgeNativeElement.classList.contains('mat-badge-above')).toBe(true);
+    expect(badgeNativeElement.classList.contains('mat-badge-after')).toBe(true);
 
-    it('should apply class based on color attribute', () => {
-      testComponent.badgeColor = 'primary';
-      fixture.detectChanges();
-      expect(badgeNativeElement.classList.contains('mat-badge-primary')).toBe(true);
+    testComponent.badgeDirection = 'below before';
+    fixture.detectChanges();
 
-      testComponent.badgeColor = 'accent';
-      fixture.detectChanges();
-      expect(badgeNativeElement.classList.contains('mat-badge-accent')).toBe(true);
+    expect(badgeNativeElement.classList.contains('mat-badge-below')).toBe(true);
+    expect(badgeNativeElement.classList.contains('mat-badge-before')).toBe(true);
+  });
 
-      testComponent.badgeColor = 'warn';
-      fixture.detectChanges();
-      expect(badgeNativeElement.classList.contains('mat-badge-warn')).toBe(true);
+  it('should change visibility to hidden', () => {
+    expect(badgeNativeElement.classList.contains('mat-badge-hidden')).toBe(false);
 
-      testComponent.badgeColor = undefined;
-      fixture.detectChanges();
+    testComponent.badgeHidden = true;
+    fixture.detectChanges();
 
-      expect(badgeNativeElement.classList).not.toContain('mat-badge-accent');
-    });
+    expect(badgeNativeElement.classList.contains('mat-badge-hidden')).toBe(true);
+  });
 
-    it('should update the badge position on direction change', () => {
-      expect(badgeNativeElement.classList.contains('mat-badge-above')).toBe(true);
-      expect(badgeNativeElement.classList.contains('mat-badge-after')).toBe(true);
+  it('should change badge sizes', () => {
+    expect(badgeNativeElement.classList.contains('mat-badge-medium')).toBe(true);
 
-      testComponent.badgeDirection = 'below before';
-      fixture.detectChanges();
+    testComponent.badgeSize = 'small';
+    fixture.detectChanges();
 
-      expect(badgeNativeElement.classList.contains('mat-badge-below')).toBe(true);
-      expect(badgeNativeElement.classList.contains('mat-badge-before')).toBe(true);
-    });
+    expect(badgeNativeElement.classList.contains('mat-badge-small')).toBe(true);
 
-    it('should change visibility to hidden', () => {
-      expect(badgeNativeElement.classList.contains('mat-badge-hidden')).toBe(false);
+    testComponent.badgeSize = 'large';
+    fixture.detectChanges();
 
-      testComponent.badgeHidden = true;
-      fixture.detectChanges();
+    expect(badgeNativeElement.classList.contains('mat-badge-large')).toBe(true);
+  });
 
-      expect(badgeNativeElement.classList.contains('mat-badge-hidden')).toBe(true);
-    });
+  it('should change badge overlap', () => {
+    expect(badgeNativeElement.classList.contains('mat-badge-overlap')).toBe(false);
 
-    it('should change badge sizes', () => {
-      expect(badgeNativeElement.classList.contains('mat-badge-medium')).toBe(true);
+    testComponent.badgeOverlap = true;
+    fixture.detectChanges();
 
-      testComponent.badgeSize = 'small';
-      fixture.detectChanges();
+    expect(badgeNativeElement.classList.contains('mat-badge-overlap')).toBe(true);
+  });
 
-      expect(badgeNativeElement.classList.contains('mat-badge-small')).toBe(true);
+  it('should toggle `aria-describedby` depending on whether the badge has a description', () => {
+    const badgeContent = badgeNativeElement.querySelector('.mat-badge-content')!;
 
-      testComponent.badgeSize = 'large';
-      fixture.detectChanges();
+    expect(badgeContent.getAttribute('aria-describedby')).toBeFalsy();
 
-      expect(badgeNativeElement.classList.contains('mat-badge-large')).toBe(true);
-    });
+    testComponent.badgeDescription = 'Describing a badge';
+    fixture.detectChanges();
 
-    it('should change badge overlap', () => {
-      expect(badgeNativeElement.classList.contains('mat-badge-overlap')).toBe(false);
+    expect(badgeContent.getAttribute('aria-describedby')).toBeTruthy();
 
-      testComponent.badgeOverlap = true;
-      fixture.detectChanges();
+    testComponent.badgeDescription = '';
+    fixture.detectChanges();
 
-      expect(badgeNativeElement.classList.contains('mat-badge-overlap')).toBe(true);
-    });
+    expect(badgeContent.getAttribute('aria-describedby')).toBeFalsy();
   });
 
 });
 
 /** Test component that contains a MatBadge. */
 @Component({
-  selector: 'test-app',
   template: `
     <span [matBadge]="badgeContent"
           [matBadgeColor]="badgeColor"
           [matBadgePosition]="badgeDirection"
           [matBadgeHidden]="badgeHidden"
           [matBadgeSize]="badgeSize"
-          [matBadgeOverlap]="badgeOverlap">
+          [matBadgeOverlap]="badgeOverlap"
+          [matBadgeDescription]="badgeDescription">
       home
     </span>
   `
 })
-class BadgeWithTextContent {
+class BadgeTestApp {
   badgeColor: ThemePalette;
   badgeContent = '1';
   badgeDirection = 'above after';
   badgeHidden = false;
   badgeSize = 'medium';
   badgeOverlap = false;
+  badgeDescription: string;
 }

src/lib/badge/badge.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Directive, Input, ElementRef, Inject, Optional, NgZone} from '@angular/core';
+import {Directive, Input, ElementRef, Inject, Optional, NgZone, OnDestroy} from '@angular/core';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
 import {ThemePalette} from '@angular/material/core';
 import {AriaDescriber} from '@angular/cdk/a11y';
@@ -33,7 +33,7 @@ export type MatBadgeSize = 'small' | 'medium' | 'large';
     '[class.mat-badge-hidden]': 'hidden',
   },
 })
-export class MatBadge {
+export class MatBadge implements OnDestroy {
 
   /** The color of the badge. Can be `primary`, `accent`, or `warn`. */
   @Input('matBadgeColor')
@@ -70,11 +70,11 @@ export class MatBadge {
   /** Message used to describe the decorated element via aria-describedby */
   @Input('matBadgeDescription')
   get description(): string { return this._description; }
-  set description(val: string) {
-    if (this._description) {
-      this._updateHostAriaDescription(val, this._description);
+  set description(newDescription: string) {
+    if (newDescription !== this._description) {
+      this._updateHostAriaDescription(newDescription, this._description);
+      this._description = newDescription;
     }
-    this._description = val;
   }
   private _description: string;
 
@@ -110,6 +110,12 @@ export class MatBadge {
     return this.position.indexOf('before') === -1;
   }
 
+  ngOnDestroy() {
+    if (this.description && this._badgeElement) {
+      this._ariaDescriber.removeDescription(this._badgeElement, this.description);
+    }
+  }
+
   /** Injects a span element into the DOM with the content. */
   private _updateTextContent(): HTMLSpanElement {
     if (!this._badgeElement) {
@@ -150,11 +156,17 @@ export class MatBadge {
   }
 
   /** Sets the aria-label property on the element */
-  private _updateHostAriaDescription(val: string, prevVal: string): void {
+  private _updateHostAriaDescription(newDescription: string, oldDescription: string): void {
     // ensure content available before setting label
     const content = this._updateTextContent();
-    this._ariaDescriber.removeDescription(content, prevVal);
-    this._ariaDescriber.describe(content, val);
+
+    if (oldDescription) {
+      this._ariaDescriber.removeDescription(content, oldDescription);
+    }
+
+    if (newDescription) {
+      this._ariaDescriber.describe(content, newDescription);
+    }
   }
 
   /** Adds css theme class given the color to the component host */